The present invention relates to a hybrid silicon wafer comprising the functions of both a polycrystalline silicon wafer and a monocrystalline wafer.
In the silicon semiconductor manufacturing process, a wafer prepared based on monocrystal growth is primarily used. This monocrystalline silicon wafer has increased in size with the times, and it is anticipated that the inner diameter thereof will become 400 mm or larger in the near future. In addition, a so-called mechanical wafer for use in testing is now required in order to establish the apparatus and peripheral technology necessary for the semiconductor manufacturing process.
Generally speaking, since this kind of mechanical wafer is subject to fairly high precision testing, it needs to possess characteristics that are similar to the mechanical physicality of a monocrystalline silicon. Thus, conventionally, although it was to be used for testing, in reality the monocrystalline silicon wafer was being used as is. However, since a monocrystalline silicon wafer having an inner diameter of 400 mm or larger is extremely expensive, an inexpensive wafer having characteristics that are similar to a monocrystalline silicon is in demand.
Meanwhile, as a component of such semiconductor manufacturing equipment, a proposal has also been made for using a sputtering target formed from a rectangular or disk-shaped silicon plate. The sputtering method is being used as a means for forming thin films, and there are several sputtering methods including the bipolar DC sputtering method, radio frequency sputtering method, magnetron sputtering method and the like, and thin films of various electronic parts are being formed using the sputtering characteristics unique to the respective methods.
This sputtering method is a method that faces a substrate as the anode and a target as the cathode, and generates an electrical field by applying a high voltage between the foregoing substrate and target under an inert gas atmosphere. Here, the ionized electrons and inert gas collide to form a plasma, the cations in the plasma collide with the target surface to hammer out the target constituent atoms, and the discharged atoms adhere to the opposite substrate surface so as to form a film.
A polycrystalline silicon sintered compact is proposed for this kind of sputtering target, and this sintered compact target is demanded of considerable thickness, large size and a rectangular or disk shape in order to improve the deposition efficiency. Moreover, a proposal has also been made for using this polycrystalline silicon sintered compact as a board for retaining the monocrystalline silicon wafer. Nevertheless, a polycrystalline silicon entails significant problems in that the sinterability is inferior, the obtained products have low density, and the mechanical strength is low.
In light of the above, in order to improve the characteristics of the foregoing silicon sintered compact, proposed is a silicon sintered compact formed by compression-molding and sintering silicon powder obtained by being heated and deoxidized under reduced pressure and within a temperature range that is 1200° C. or higher and less than the melting point of silicon, and setting the crystal grain size of the sintered compact to be 100 μm or less (for instance, refer to Patent Document 1).
If the thickness of the silicon sintered compact manufactured as described above is thin; for instance, 5 mm or less, the density will relatively increase and the strength will also increase, however, the thickness becomes much thicker the density will continue to be a low density (less than 99%), and the mechanical strength will also deteriorate. Thus, there is a problem in that manufacturing a large-size rectangular or disk-shaped silicon sintered compact is not possible.
In light of the foregoing circumstances, the present applicant previously proposed a silicon sintered compact and its production method in which the average crystal grain size is 50 μm or less and the relative density is 99% or more (refer to Patent Document 2).
Although this silicon sintered compact possesses numerous advantages including high density and high mechanical strength, the further improvement of these characteristics is being demanded, and the applicant filed a patent application relating to technology that improved the foregoing points.
Since a wafer using the foregoing silicon sintered compact has similar mechanical properties as a monocrystalline silicon, it can be used as a dummy wafer for the transport system of semiconductor manufacturing equipment or the development of robotics. In addition, the application of an SOI wafer as a base substrate is also being considered.
Nevertheless, these are all polycrystalline silicons made from a silicon sintered compact, and although there are numerous points that are similar to the physical properties of a monocrystal, they do not possess the functions as the monocrystal itself, and there is a fundamental problem in that they cannot be used for process testing such as deposition experiments.
There is also a proposal of manufacturing a high quality polycrystalline silicon in substitute for a monocrystalline silicon (refer to Patent Document 3). Nevertheless, a polycrystalline silicon has a drawback in that, no matter what kind of devisal is made, its characteristics will be inferior to a monocrystalline silicon.
Moreover, with respect to the patent application that was previously filed by the applicant, since a sintered silicon is used at a polycrystalline portion, the crystal orientation becomes random, and there is a problem in that unevenness occurs during the grinding process, and a problem in that a large amount of gas component impurities will be included (refer to Patent Document 4).    [Patent Document 1] Japanese Patent No. 3342898    [Patent Document 2] Japanese Patent No. 3819863    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2005-132671    [Patent Document 4] Japanese Patent Application No. 2008-179988